1. Field of the Invention
This invention relates to a process for calcining a denitrating catalyst. More particularly, it relates to a process for calcining a denitrating catalyst to obtain a denitrating catalyst which provides a uniform performance.
2. Description of the Related Art
Heretofore, catalysts composed mainly of oxides of metals such as titanium, vanadium, molybdenum, etc. have been used in connection with exhaust gas-denitration. During exhaust gas denitration, nitrogen oxides contained in exhaust gases are reduced with ammonia. These metal oxide catalysts are molded products having low strength. Thus, a process to form a plate catalyst has been developed and is set forth in U.S. Pat. No. 4,567,630. In that process, a catalytic substance is applied onto both the surfaces of a core porous plate support to form a plate catalyst.
In one example of porous plate catalyst preparation, a raw material slurry of a catalytic substance is heat-kneaded, followed by extrusion-granulation, drying, precalcination, milling, thereafter adding water and a filler, kneading the mixture in a pasty state, applying the resulting material onto a plate expanded metal, contact-bonding these, processing the resulting material into a plate shape having Z-form projections in the cross-section, cutting and air-drying. The resulting plate catalyst elements are calcined, and then impregnated with another catalytic component, if necessary. They are then stacked within a frame body to form a catalyst unit. This catalyst unit is then subjected to final calcination to form a product.
The calcining furnace used for the above-mentioned calcination is a so-called hot air circulating furnace. In the past, it has been know to circulate hot air in only one direction through the catalyst units arranged on a track within the furnace.
The furnace however, has raised problems in that the performance of the product obtained after the calcination is not constant. In particular, the catalyst on the inlet side of the hot air furnace and that on the exit side thereof are of inferior quality. They make it undesirable to use such catalyst. Furthermore, not only does the available volume of the hot air furnace become reduced, but the amount of energy loss increases, and an extended calcination time is required.